1. Technical Field
The present invention relates to an optical element including a half mirror and a display apparatus including an optical element.
2. Related Art
In a head mounted display in which both of image information emitted from an image light emitting device and image information on the external environment can be observed in the same visual field, image light is reflected toward eyes of an observer and a half mirror which allows the light from the external environment to be transmitted to the eyes of the observer is used.
As the half mirror, for example, a configuration in which a metal thin film is interposed between translucent films is proposed (see U.S. Pat. No. 3,559,090 and Japanese Patent No. 3563955). In addition, in Japanese Patent No. 3563955, layer configurations of a substrate/silicon oxide layer/zirconium oxide layer or a titanium oxide layer/chrome layer/silver layer/aluminum oxide layer/zirconium oxide layer/silicon oxide layer are proposed.
In the half mirror disclosed in Japanese Patent No. 3563955, since a chrome layer is formed as a base layer of a silver layer for improving an adhesion property or the like with a lower layer side of the silver layer, there is a problem in that a loss in light quantity due to the chrome layer is large. Further, in a case of using a resin substrate as a substrate, even when the chrome layer is omitted after the problem of the adhesion property of the silver layer is solved, there is a problem in that the density of the silver layer or a dielectric film decreases due to the influence of moisture adsorbed by the resin substrate and an organic component desorbed from the resin substrate, so optical characteristics are degraded due to diffusion of silver particles or modification of the silver layer.